Display device and electronic device

ABSTRACT

A display device capable of displaying a picture of vivid colors maintaining a good balance of colors and a good balance of light-emitting brightnesses of the EL elements. The widths of the detour wirings supplying current to the power source feed lines are increased for those EL elements into which a current of a large density flows. This constitution decreases the wiring resistances of the detour wirings, decreases the potential drop through the detour wirings, and suppresses the amount of electric power consumed by the detour wirings.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an EL (electroluminescence) display device (alight emitting device or a light emitting diode or OLED (Organic LightEmission Diode) formed by fabricating semiconductor elements (elementsusing a thin semiconductor film) on a substrate, and to an electronicdevice which uses the EL display device for a display unit thereof. TheEL devices referred to in this specification include triplet-based lightemission devices and/or singlet-based light emission devices, forexample.

2. Related Art

In recent years, technology for forming TFTs on a substrate has greatlyadvanced and study has been forwarded to apply the technology to theactive matrix-type display devices. In particular, study has beenvigorously forwarded concerning the active matrix-type EL display deviceusing EL elements as spontaneously light-emitting elements among theactive matrix type display devices. The EL display device is also calledorganic EL display (OELD) or organic light-emitting diode (OLED).

Unlike liquid crystal display devices, the EL display device is the onethat spontaneously emits light. The EL element has a structure in whichan EL layer is held between a pair of electrodes, the EL layer being,usually, of a laminated layer structure. The laminated-layer structurecan be represented by a “positive hole-transporting layer/light emittinglayer/electron-transporting layer” proposed by Tang et al. of EastmanKodak Co. This structure features a very high light-emitting efficiency,and almost all of the EL display devices that have now been studied anddeveloped are employing this structure.

Luminescence of the organic EL material stems from the emission of light(fluorescence) of when a singlet excited state returns back to theground state or stems from the emission of light (phosphorescence) ofwhen a triplet excited state returns back to the ground state. The ELelement of this invention may utilize either one of the above-mentionedtype of light emission or may utilize both of the above-mentioned typesof light emission.

In addition to the above, there can be further employed a lamination ofpositive hole-injection layer/positive hole-transportinglayer/light-emitting layer/electron transporting layer or a laminationof positive hole-injection layer/positive hole-transportinglayer/light-emitting layer/electron-transportinglayer/electron-injection layer on the pixel electrode. The EL layer maybe doped with a fluorescent coloring matter.

A predetermined voltage is applied to the thus constituted EL layer froma pair of electrodes, whereby the carriers are recombined together inthe light-emitting layer to emit light. In this specification, the ELelement is called to have been driven when it emits light.

In this specification, the light-emitting element formed by an anode, anEL layer and a cathode is called EL element.

FIG. 14 illustrates the structure of a representative active matrix-typeEL display device (hereinafter referred to as EL display device),wherein FIG. 14(A) shows the arrangement of a pixel unit of the ELdisplay device and a drive circuit therefor. Reference numeral 901denotes a pixel unit, 902 denotes a source signal line drive circuit,903 denotes a gate signal line drive circuit, and 905 denotes draw-outterminals.

The pixel unit 901 includes plural pixels 906. Reference numeral 904denotes power source feed lines formed on the pixel unit 901 to apply apotential to the pixel electrodes of the EL elements possessed by allpixels 906. Power source feed lines 904 are connected to detour wirings907 which are connected to an external power source via draw-outterminals 905.

Pixels 906 are selected by select signals input to gate signal lines 913from the gate signal line drive circuit 903. The potential of the powersource feed lines 904 is given to the selected pixels 906 due to videosignals input to the source signal line 912 from the source signal linedrive circuit 902, and the pixels 906 display part of the picture.

FIG. 14(B) is a circuit diagram of pixels corresponding to R (red), G(green) and B (blue) among the pixels 906 shown in FIG. 14(A).

In FIG. 14(B), a pixel 906 r for R, a pixel 906 g for G and a pixel 906b for B have a common gate signal line 913. Further, the pixel 906 r forR has a source signal 912 r for R, the pixel 906 g for G has a sourcesignal line 912 g for G, and the pixel 906 b for B has a source signalline 912 b for B.

The pixel 906 r for R, the pixel 906 g for G and the pixel 906 b for Bhave a switching TFT 910 and an EL drive TFT 911, respectively. Further,the pixel 906 r for R has an EL element 915 r for R, the pixel 906 g forG has an EL element 915 g for G, and the pixel 906 b for B has an ELelement 915 b for B.

When a select signal is input to the gate signal line 913, the switchingTFTs 910 connected at their gate electrodes to the gate signal line 913are all turned on. In this specification, this state is referred to asthat the gate signal line 913 is selected.

Video signals input to the source signal line 912 r for R, to the sourcesignal line 912 g for G and to the source signal line 912 b for B, arefurther input to the EL element 915 r for R, to the EL element 915 g forG and to the EL element 915 b for B through the switching TFTs 910 whichhave been turned on, so as to be input to the gate electrodes of the ELdrive TFTs 911.

When the video signals are input to the gate electrodes of the EL driveTFTs 911, the potential of the power source feed line 914 r for R isapplied to the pixel electrode of the EL element 915 r for R, thepotential of the power source feed line 914 g for G is applied to thepixel electrode of the EL element 915 g for G, and the potential of thepower source feed line 914 b for B is applied to the pixel electrode ofthe EL element 915 b for B. As a result, the EL element 915 r for R, theEL element 915 g for G and the EL element 915 b for B emit light, and adisplay is produced by the pixel 906 r for R, by the pixel 906 g for Gand by the pixel 906 b for B.

The EL display devices can be roughly divided into those of the fourcolor display systems, such as those of the system shown in FIG. 14forming EL elements of three kinds of organic EL materials correspondingto R (red) G (green) and B (blue), those of the system in which whitelight-emitting EL elements and color filters are combined together,those of the system in which blue or bluish green light-emitting ELelements and a fluorescent material (fluorescent color-conversion layer:CCM) are combined together, and those of the system in which EL elementscorresponding to RGB are stacked by using transparent electrodes for thecathodes (opposing electrodes).

In general, even when the same voltage is applied to the EL layer, thelight-emitting brightness of the EL layer differs depending upon theorganic EL material used for the EL layer. FIG. 15 illustrates voltagebrightness characteristics of the EL layers of each of the colors. Asshown in FIG. 15, the light-emitting brightness of the EL layer to theapplied voltage, varies depending upon the organic EL materials used forthe EL elements of each of the colors. This is because the currentdensity of when the same voltage is applied differs depending upon theorganic EL materials.

Even when the current density remains the same, the light-emittingbrightness differs depending upon the organic EL materials.

In the EL display device, therefore, the potentials of the power sourcefeed lines for the pixels of each of the colors are usually adjusted tomaintain a balance in the light-emitting brightness of the EL elementsof three colors.

The magnitude of electric current flowing into the pixel unit throughthe detour wiring is deter mined by the number of pixels producing awhite display in the pixel unit. The pixels producing the white displaystand for those pixel elements having an EL element which is in alight-emitting state. The electric current that flows into the pixelunit via the detour wiring increases with an increase in the number ofthe pixels producing the white display.

An increase in the current flowing through the detour wiring results ina drop in the potential through the detour wiring. Therefore, thevoltage applied to each EL element becomes small and the light-emittingbrightness of each pixel decreases when an increased number of pixelsare producing the white display.

In the case of the color EL display device, in particular, the voltagesapplied to the EL elements of each of the colors are adjusted to changethe magnitudes of current flowing into the EL elements of each of thecolors. An increase in the currents flowing into the pixels results inan increase in the drop of potential through the detour wirings to thecorresponding pixels. Therefore, even when the voltages applied to theEL elements of each of the colors are adjusted, the ratio of currentsflowing into the EL elements of three colors changes depending uponwhether the number of the pixels producing the white display is large ornot.

A change in the number of the pixels producing the white display invitesa loss of balance in the light-emitting brightness of the pixelscorresponding to the three colors.

In the conventional EL display device, the magnitude of current thatflows into the EL elements changes depending upon the colors, anddifferent voltages are applied to the EL elements. However, the EL driveTFTs provided as switching elements between the EL elements and thepower source feed lines have the same LDD width and the same channelwidth and, besides, voltages of the digital signals input to the gateelectrodes of all EL drive TFTs have the same amplitude. Accordingly,the EL drive TFTs are deteriorated by the magnitudes of voltages appliedto the power source feed lines. Besides, when the amplitudes of voltagesof digital signals input to the gate electrodes of the EL drive TFT gateelectrodes are too great, it becomes difficult to suppress theconsumption of electric power.

SUMMARY OF THE INVENTION

In view of the above-mentioned problems, this invention provides an ELdisplay device capable of producing a highly fine color display.

The present inventors have attempted to increase the widths of thedetour wirings for those EL elements for which an increased current isto be supplied. Therefore, the wiring resistance of the detour wiringsdecreases for those pixels to which a large current is to be supplied.As the wiring resistance decreases, a drop of potential through thedetour wirings decreases, and a large current can be supplied to the ELelements. In the practical panel, limitation is imposed on space forlaying the detour wirings. By changing the ratio of widths of the detourwirings for each of the colors, therefore, it is allowed to maintain abalance in the magnitudes of currents flowing into the EL elements ofeach of the colors.

Owing to the above constitution, therefore, it is allowed to maintain abalance in the light emitting brightness of the pixels of R, G and Birrespective of the number of pixels producing the white display.

Further, if not only the detour wirings but also the widths of the powersource feed lines are increased for those EL elements of pixels to whichlarge currents are to be supplied, it becomes possible to produce a morehighly fine picture.

In this invention, further, the amplitude of the video signals may beincreased only for those pixels whose EL elements are to be suppliedwith a large current. Owing to the above constitution, video signals oftoo large amplitudes need not be input to all of the pixels, and theconsumption of electric power can be suppressed.

Further, the EL drive TFTs for controlling the flow of current to the ELelements permit the flow of a current larger than the current permittedto flow through the switching TFTs that control the EL drive TFTs, sothat the EL elements emit light. Here, controlling the TFTs is equal tocontrolling the voltage applied to the gate electrodes possessed by theTFTs, and has the meaning of turning the TFTs on or off. In thisinvention constituted as described above, in particular, a large currentflows into the EL drive TFTs in the pixels connected to the power sourcefeed lines through which a current of a large absolute value flows.Accordingly, there arises a problem in that the EL drive TFTs of thepixels connected to the power source feed lines through which a currentof a large absolute value flows, are deteriorated earlier than the ELdrive TFTs of other pixels due to the injection of hot carriers.

To cope with the deterioration of the EL drive TFTs caused by theinjection of hot carriers according to the invention, therefore, thelengths of the LDD regions of the EL drive TFTs of the pixels fordisplaying a color of a low light emitting brightness may be selected tobe larger than the lengths of the LDD regions of the EL drive TFTs ofthe pixels for displaying a color of a high light-emitting brightness,in addition to adopting the above-mentioned constitution.

In this specification, the lengths of the LDD regions are the lengths ofthe LDD regions in a direction of connecting the source regions to thedrain regions.

At the same time, further, the channel width (W) may be increased in theEL drive TFTs of pixels which are connected to the power source feedlines having a large absolute current value.

FIG. 5 shows a top view and a sectional view of a representative TFT.FIG. 5(A) is a top view of TFT, and FIG. 5(B) is a sectional view alongA-A′ in FIG. 5(A).

Reference numeral 501 denotes a source region, 502 denotes a drainregion, and 503 denotes a gate electrode. A channel-forming region 504is formed under the gate electrode 503 via a gate-insulating film 505.In this specification, the channel width (W) stands for a length of thechannel region 504 in a direction perpendicular to the direction ofcurrent that flows between the source region 501 and the drain region502. Further, the channel length (L) stands for a length of the channelregion 504 in the direction in which the current flows into the sourceregion 501 and the drain region 502.

According to the above-mentioned constitution of the invention, the ELdrive TFTs are suppressed from being deteriorated even when the currentcontrolled by the EL drive TFTs has increased due to an increase in theabsolute value of current flowing through the power source feed lines.It is further allowed to adjust the light-emitting brightness of the ELelement relying on the voltage applied to the EL element and, hence, todisplay a picture of vivid colors maintaining a good balance in thelight-emitting brightnesses of red color, blue color and green color.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) and 1(B) are diagrams illustrating the constitution of an ELdisplay device according to this invention;

FIG. 2 is a diagram illustrating the constitution of a pixel in the ELdisplay device;

FIG. 3 is a block diagram of a source signal line drive circuit in theEL display device of this invention;

FIG. 4 is a diagram of an equivalent circuit of a level shifter circuit;

FIGS. 5(A) and 5(B) include a top view and a sectional view of a TFT;

FIGS. 6(A) and 6(B) are circuit diagrams of a pixel in the EL displaydevice;

FIGS. 7(A) and 7(B) are circuit diagrams of the pixel in the EL displaydevice;

FIGS. 8(A) to 8(C) are views illustrating the steps of fabricating theEL display device;

FIGS. 9(A) to 9(C) are views illustrating the steps of fabricating theEL display device;

FIGS. 10(A) to 10(B) are diagrams illustrating the steps of fabricatingthe EL display device;

FIG. 11 is a diagram illustrating the steps of fabricating the ELdisplay device;

FIGS. 12(A) to 12(F) are views illustrating concrete examples of theelectronic devices;

FIGS. 13(A) and 13(B) are views illustrating concrete examples of theelectronic devices;

FIGS. 14(A) and 14(B) are diagrams illustrating the constitution of aconventional EL display device;

FIG. 15 is a diagram illustrating voltage-brightness characteristics ofan organic EL material;

FIGS. 16(A) and 16(B) are top views of a TFT substrate in the EL displaydevice of this invention;

FIGS. 17(A) to 17(C) include a perspective view and a sectional view ofthe EL display device of this invention;

FIGS. 18(A) to 18(C) are diagrams illustrating the steps of fabricatingthe EL display device of this invention; and

FIGS. 19(A) and 19(B) are sectional views of the EL display device usinga DLC film of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a top view of an EL display device of this invention, and FIG.1(A) illustrates the arrangement of a pixel unit and a drive circuit inthe EL display device, wherein reference numeral 101 denotes a pixelunit, 102 denotes a source signal line drive circuit, 103 denotes a gatesignal line drive circuit, and 105 denotes draw-out terminals.

The pixel unit 101 has plural pixels 106. Reference numeral 104 denotespower source feed lines provided in the pixel unit 101 to give potentialto the pixel electrodes of the EL elements possessed by all of thepixels 106. The power source feed lines 104 are connected to detourwirings 107 which are connected to an external power source via thedraw-out terminals 105. The layout of the detour wirings 107 is in noway limited to the form shown in FIG. 1.

Pixels 106 are selected by select signals input to the gate signal lines(not shown) from the gate signal line drive circuit 103. In response tovideo signals input to the source signal lines (not shown) from thesource signal line drive circuit 102, the potential of the power sourcefeed lines 104 is given to the selected pixels 106 which, then, displaya part of a picture.

FIG. 1(B) is a diagram illustrating, on an enlarged scale, the detourwirings 107 of FIG. 1(A), and wherein reference numeral 107 r denotes adetour wiring for R, 107 g denotes a detour wiring for G and 107 bdenotes a detour wiring for B.

The EL element is connected in series with the detour wirings.Therefore, a ratio of currents flowing through the detour wiringscorresponding to the colors RGB corresponds to a ratio of currentdensities through the EL layers corresponding to the colors RGB. Ingeneral, further, the wiring resistance varies in proportion to thesheet resistance and the length of the wiring, but varies in reverseproportion to the width of the wiring. Here, the sheet resistance andthe length of the wiring are constant.

Here, the voltage applied to the detour wiring for R is denoted by Vr,the voltage applied to the detour wiring for G is denoted by Vg, thevoltage applied to the detour wiring for B is denoted by Vb, the widthof the detour wiring for R is denoted by Wr, the width of the detourwiring for G is denoted by Wg, the width of the detour wiring for B isdenoted by Wb, the current density of the EL element for R is denoted byIr, the current density of the EL element for G by Ig and the currentdensity of the EL element for B by Ib. Then, the following formula 1holds from Ohms' law. Here, a is a constant.

Vr=a×Ir/Wr

Vg=a×Ig/Wg

Vb=a×Ib/Wb  (1)

Here, if Vr=Vg=Vb, then, the following formula 2 is derived,

Ir/Wr=Ig/Wg=Ib/Wb  (2)

From the formula 2 is derived the following formula 3,

Wr:Wg:Wb=Ir:Ig:Ib  (3)

From the formula 3, therefore, in order to maintain a balance in thelight-emitting brightness of the pixels R, G and B, the width of thedetour wirings electrically connected to the EL elements of largecurrent densities is selected to be larger than the width of the detourwirings electrically connected to the EL elements having small currentdensities. Desirably, the ratio of widths of the detour wirings isselected to satisfy the formula 3.

Not only the detour wirings but also the power source feed lines forfeeding voltages or currents to the EL elements of the pixels may be sodesigned as to possess widths that satisfy the formula 3 for the pixelsfor which large currents are to be supplied, in order to display a morehighly fine picture.

Owing to the above constitution, it is allowed to maintain a balance inthe light-emitting brightness of the pixels R, G and B.

EMBODIMENTS Embodiment 1

In this embodiment, the amplitude of the digital signals is increasedfor those pixels that require large voltages for the EL elements.

FIG. 2 schematically illustrates the constitution of connection betweenthe EL drive TFT and the EL element in the pixel in the EL displaydevice, and wherein reference numeral 202 denotes an EL drive TFT, 203denotes a power source feed line, and 206 denotes an EL element. Thegate electrode of the EL drive TFT 202 receives a digital signal that isgiven to a terminal 201. The source region of the EL drive TFT 202 isconnected to the power source feed line 203, and the drain regionthereof is connected to a pixel electrode possessed by the EL element206.

If the absolute value of the current given to the power source feed line203 is increased to increase the light emitting brightness of the ELelement, the off current of the EL drive TFT 202 (current that flows ina state where the TFT is turned off) increases. Therefore, it may happenthat the EL element emits light even in a state where the EL drive TFT202 is turned off.

In this invention, the amplitude of the digital signals is increased forthose pixels to which a current having a large absolute value issupplied from the power source feed line (concretely speaking, in thecase of FIG. 2, digital signals of a large amplitude are input to theterminal 201). Since the amplified digital signals are input to the gateelectrodes of the EL drive TFTs 202, |V_(GS)| of the EL drive TFT 202becomes larger than that of before the digital signal was amplified.Even by increasing the absolute value of the current of the power sourcefeed line 203, therefore, the off current of the EL drive TFT 202 can besuppressed, preventing such an occurrence that the EL element emitslight even in a state where the EL drive TFT 202 is turned off.

The invention is not limited to the EL display device which displays apicture by using digital signals only but may also be applied to an ELdisplay device which displays a picture by using analog signals.

Embodiment 2

This embodiment deals with a concrete constitution of the source signalline drive circuit used in the embodiment 1.

FIG. 3 is a block diagram of a source signal line drive circuitaccording to this embodiment, and wherein reference numeral 400 denotesa pixel unit, and 401 denotes a source signal line drive circuit. Thesource signal line drive circuit 401 includes a shift register circuit402, a first latch circuit 403, a second latch circuit 404, a levelshifter circuit 405 and a buffer circuit 406.

A digital signal (DV) is input to the first latch circuit 403 from theoutside of the source signal line drive circuit 401 and is held thereinaccording to a timing signal (TS) formed by the shift register circuit402. When the digital signals of all bits are input and held in thefirst latch circuit 403, the digital signals held in the first latchcircuit 403 are input to the second latch circuit 404 at one time andare held therein according to a latch pulse (LP). The operation startsagain in which a digital signal (DV) is input to the first latch circuit403 from outside the source signal line drive circuit 401 and is heldtherein.

The digital signals input at one time to the second latch circuit 404and are held therein, are further input to the level shifter circuit 405and are output therefrom after their amplitudes are amplified. Themagnitude of amplification differs in each of the pixels which receivedigital signals depending upon the absolute value of the current flowingthrough the power source feed lines. The amplitude of the digital videosignal is increased for those pixels which receive the video signal andfor which the current having a large absolute value is supplied from thepower source feed lines.

By changing the output voltage of the level shifter circuit, i.e., bychanging the power source potential of the level shifter circuit, it isallowed to change the amplitude of the digital signals input to thepixels for each of the colors.

Even by increasing the absolute value of current flowing through thepower source feed lines relying upon the above constitution, it isallowed to suppress the off current of the EL drive TFTs preventing suchan occurrence that light is emitted by the EL elements even in a statewhere the EL drive TFTs are turned off.

The amplified digital signals output from the level shifter circuit 405are buffer-amplified through the buffer circuit 406 and are input to thecorresponding source signal lines.

FIG. 4 is an equivalent circuit diagram of a level shifter circuit 405.A digital signal is input through Vin of the level shifter circuit 405.A signal obtained by inverting the polarity of the digital signal isinput through Vinb. Symbol Vddh denotes a connection to the power sourceof the high voltage side, and Vss denotes a connection to the powersource of the low voltage side.

The level shifter circuit 403 is so designed that a signal obtained byamplifying the digital signal input to Vin is output from Vout.Concretely speaking, when a digital signal Hi is input to Vin, a signalcorresponding to Vss is output from Vout and when a digital signal Lo isinput thereto, a signal corresponding to Vddh is output from Vout.

Embodiment 3

This embodiment deals with concrete numerical values of the widths ofthe detour wirings 107 shown in FIG. 1.

In this embodiment, the current densities through the organic ELmaterials of R, G and B are selected to be 7.5 mA/cm², 3 mA/cm² and 5mA/cm² so that the light-emitting brightnesses of the EL elements of R,G and B become 100 cd/m², 100 cd/m² and 50 cd/m².

From the above current densities and in compliance with the formula 3,the ratio of widths of the power source feed lines for the pixelscorresponding to R, G and B becomes as given by the formula 4,

Wr:Wg:Wb=7.5:3:5  (4)

The balance in the light-emitting brightnesses of the pixels R, G, B canbe maintained upon designing the widths of the detour wirings inaccordance with the formula 4.

In this embodiment, the widths of the detour wirings corresponding to R,G and B need not satisfy the formula 4. The width of the detour wiringcorresponding to R may be selected to be the greatest and the width ofthe detour wiring corresponding to G may be selected to be the smallest.

The above constitution makes it possible to adjust the balance oflight-emitting brightnesses of the pixels R, G and B irrespective of thenumber of the pixels producing the white display.

The balance of the light-emitting brightnesses of the pixels R, G and Bcan be more effectively adjusted if the width of the power source feedlines for R is selected to be the greatest and the width of the powersource feed lines for G to be the smallest in addition to the detourwirings. The balance in the light-emitting brightnesses of the pixels R,G and B can be more favorably adjusted if the widths of the power sourcefeed lines are so designed as to satisfy the formula 4 like the detourwirings.

The current densities of the organic EL materials used in this inventionare not limited to the above-mentioned numerical values only.

Though the Example has dealt with the case of amplifying the amplitudeof digital signals in the EL display device which produces the displayrelying on the digital signals, the invention is in no way limited tothis constitution only. The invention encompasses even the constitutionof amplifying the amplitude of the analog video signals in the ELdisplay device that produces the display relying on the analog videosignals.

It is further allowable to carryout this embodiment in free combinationwith the embodiment 1 or the embodiment 2.

Embodiment 4

In the EL display device of this invention, many TFTs may be provided ineach pixel. For example, three to six or more TFTs may be provided. Thisembodiment deals with the EL display device in which three TFTs areprovided in each pixel.

In FIG. 6, reference numeral 4702 denotes a switching TFT, 4701 denotesa source signal line, 4703 denotes a gate signal line connected to thegate electrode of the switching TFT 4702, 4704 denotes an EL drive TFT,4705 denotes a capacitor (which may not be provided), 4706 denotes apower source feed line, 4707 denotes a power source control TFT, 4708denotes a gate signal line for controlling the power source, and 4709denotes an EL element. As for the operation of the power source controlTFT 4707, reference should be made to Japanese Patent Application No.364003/2000.

In this embodiment, further, the electric power control TFT 4707 isprovided between the EL drive TFT 4704 and the EL element 4708. It is,however, also allowable to provide the EL driving TFT 4704 between thepower source control TFT 4707 and the EL element 4708. It is furtherdesired that the power source control TFT 4707 has the same structure asthe EL drive TFT 4704 or is formed in series therewith using the sameactive layer.

In FIG. 7, reference numeral 4801 denotes a source signal line, 4802denotes a switching TFT, 4803 denotes a gate signal line connected tothe gate electrode of the switching TFT 4802, 4804 denotes an EL drivingTFT, 4805 denotes a capacitor (which may not be provided), 4806 denotesa power source feed line, 4807 denotes an erasing TFT, 4808 denotesagate signal line for erasing, and 4809 denotes an EL element. As forthe operation of the erasing TFT 4807, reference should be made toJapanese Patent Application No. 359032/2000.

The drain of the erasing TFT 4807 is connected to the gate of the ELdriving TFT 4804 to forcibly change the gate voltage of the EL drivingTFT 4804. Here, the erasing TFT 4807 may be an n-channel TFT or ap-channel TFT but should desirably have the same structure as theswitching TFT 4802 to decrease the off current.

This embodiment can be carried out in free combination with theembodiments 1 to 3.

Embodiment 5

In this embodiment, in the EL display device of the present invention, amethod of simultaneously forming, on the same substrate, a pixel portionand TFTs (n-channel TFT and p-channel TFT) of a driving circuit providedin the periphery of the pixel portion, is described in detail with FIGS.8A to 11B.

First, in this embodiment, a substrate 300 is used, which is made ofglass such as barium borosilicate glass or aluminum borosilicate,represented by such as Corning #7059 glass and #1737 glass. Note that,as the substrate 300, there is no limitation provided that it is asubstrate with transmittance, and a quartz substrate may be used. Aplastic substrate with heat resistance to a process temperature of thisembodiment may also be used.

Then, a base film 301 formed of an insulating film such as a siliconoxide film, a silicon nitride film or a silicon nitride oxide film isformed on the substrate 300. In this embodiment, a two-layer structureis used as the base film 301. However, a single-layer film or alamination structure consisting of two or more layers of the insulatingfilm may be used. As a first layer of the base film 301, a siliconnitride oxide film 301 a is formed with a thickness of 10 to 200 nm(preferably 50 to 100 nm) with a plasma CVD method using SiH₄, NH₃, andN₂O as reaction gas. In this embodiment, the silicon nitride oxide film301 a (composition ratio Si=32%, O=27%, N=24% and H=17%) with a filmthickness of 50 nm is formed. Then, as a second layer of the base film301, a silicon nitride oxide film 301 b is formed and laminated into athickness of 50 to 200 nm (preferably 100 to 150 nm) with a plasma CVDmethod using SiH₄ and N₂O as reaction gas. In this embodiment, thesilicon nitride oxide film 301 b (composition ratio Si=32%, O=59%, N=7%and H=2%) with a film thickness of 100 nm is formed.

Subsequently, semiconductor layers 302 to 305 are formed on the basefilm. The semiconductor layers 302 to 305 are formed from asemiconductor film with an amorphous structure which is formed by aknown method (such as a sputtering method, an LPCVD method, or a plasmaCVD method), and is subjected to a known crystallization process (alaser crystallization method, a thermal crystallization method, or athermal crystallization method using a catalyst such as nickel). Thecrystalline semiconductor film thus obtained is patterned into desiredshapes to obtain the semiconductor layers. The semiconductor layers 302to 305 are formed into the thickness of from 25 to 80 nm (preferably 30to 60 nm). The material of the crystalline semiconductor film is notparticularly limited, but it is preferable to be formed of silicon, asilicon germanium (Si_(x)Ge_(1-x) (X=0.0001 to 0.02)) alloy, or thelike. In this embodiment, 55 nm thick amorphous silicon film is formedby a plasma CVD method, and then, a nickel-containing solution is heldon the amorphous silicon film. A dehydrogenation process of theamorphous silicon film is performed (500° C. for one hour), andthereafter a thermal crystallization process is performed (550° C. forfour hours) thereto. Further, to improve the crystallinity thereof, alaser annealing treatment is performed to form the crystalline siliconfilm. Then, this crystalline silicon film is subjected to a patterningprocess using a photolithography method, to obtain the semiconductorlayers 302 to 305.

Further, after the formation of the semiconductor layers 302 to 305, aminute amount of impurity element (boron or phosphorus) may be doped tocontrol a threshold value of the TFT.

Besides, in the case where the crystalline semiconductor film ismanufactured by the laser crystallization method, a pulse-oscillationtype or continuous-wave type excimer laser, YAG laser, or YVO₄ laser maybe used. In the case where those kinds of laser are used, it isappropriate to use a method in which laser light radiated from a laseroscillator is condensed by an optical system into a linear beam, and isirradiated to the semiconductor film. Although the conditions of thecrystallization should be properly selected by an operator, in the casewhere the excimer laser is used, a pulse oscillation frequency is set as300 Hz, and a laser energy density is set as 100 to 400 mJ/cm²(typically 200 to 300 mJ/cm²). In the case where the YAG laser is used,it is appropriate that the second harmonic is used to with a pulseoscillation frequency of 30 to 300 kHz and a laser energy density of 300to 600 mJ/cm² (typically, 350 to 500 mJ/cm²). Then, laser lightcondensed into a linear shape with a width of 100 to 1000 μm, forexample, 400 μm is irradiated to the whole surface of the substrate, andan overlapping ratio (overlap ratio) of the linear laser light at thistime may be set as 50 to 90%.

A gate insulating film 306 is then formed for covering the semiconductorlayers 302 to 305. The gate insulating film 306 is formed of aninsulating film containing silicon by a plasma CVD method or asputtering method into a film thickness of from 40 to 150 nm. In thisembodiment, the gate insulating film 306 is formed of a silicon nitrideoxide film into a thickness of 110 nm by a plasma CVD method(composition ratio Si=32%, O=59%, N=7%, and H=2%). Of course, the gateinsulating film is not limited to the silicon nitride oxide film, and another insulating film containing silicon may be used as a single layeror a lamination structure.

Besides, when the silicon oxide film is used, it can be possible to beformed by a plasma CVD method in which TEOS (tetraethyl orthosilicate)and O₂ are mixed and discharged at a high frequency (13.56 MHZ) powerdensity of 0.5 to 0.8 W/cm² with a reaction pressure of 40 Pa and asubstrate temperature of 300 to 400° C. Good characteristics as the gateinsulating film can be obtained in the manufactured silicon oxide filmthus by subsequent thermal annealing at 400 to 500° C.

Then, as shown in FIG. 8A, on the gate insulating film 306, a firstconductive film 307 with a thickness of 20 to 100 nm and a secondconductive film 308 with a thickness of 100 to 400 nm are formed andlaminated. In this embodiment, the first conductive film 307 of TaN filmwith a film thickness of 30 nm and the second conductive film 308 of a Wfilm with a film thickness of 370 nm are formed into lamination. The TaNfilm is formed by sputtering with a Ta target under a nitrogencontaining atmosphere. Besides, the W film is formed by the sputteringmethod with a W target. The W film may be formed by a thermal CVD methodusing tungsten hexafluoride (WF₆). Whichever method is used, it isnecessary to make the material have low resistance for use as the gateelectrode, and it is preferred that the resistivity of the W film is setto less than or equal to 20 μΩcm. By making the crystal grains large, itis possible to make the W film have lower resistivity. However, in thecase where many impurity elements such as oxygen are contained withinthe W film, crystallization is inhibited and the resistance becomeshigher. Therefore, in this embodiment, by forming the W film by asputtering method using a W target with a purity of 99.9999% or 99.99%,and in addition, by taking sufficient consideration to preventimpurities within the gas phase from mixing therein during the filmformation, a resistivity of from 9 to 20 μΩcm can be realized.

Note that, in this embodiment, the first conductive film 307 is made ofTaN, and the second conductive film 308 is made of W, but the materialis not particularly limited thereto, and either film may be formed of anelement selected from the group consisting of Ta, W, Ti, Mo, Al, Cu, Cr,and Nd, or an alloy material or a compound material containing the aboveelement as its main constituent. Besides, a semiconductor film, typifiedby a polycrystalline silicon film doped with an impurity element such asphosphorus, may be used Further, an AgPdCu alloy may be used. Besides,any combination may be employed such as a combination in which the firstconductive film is formed of tantalum (Ta) and the second conductivefilm is formed of W, a combination in which the first conductive film isformed of titanium nitride (TiN) and the second conductive film isformed of W, a combination in which the first conductive film is formedof tantalum nitride (TaN) and the second conductive film is formed ofAl, or a combination in which the first conductive film is formed oftantalum nitride (TaN) and the second conductive film is formed of Cu.

Next, masks 309 to 312 made of resist are formed using aphotolithography method as shown in FIG. 8B, and a first etching processis performed in order to form electrodes and wirings. This first etchingprocess is performed with the first and second etching conditions. Inthis embodiment, as the first etching conditions, an ICP (inductivelycoupled plasma) etching method is used, a gas mixture of CF₄, Cl₂ and O₂is used as an etching gas, the gas flow rate is set to 25/25/10 sccm,and plasma is generated by applying a 500 W RF (13.56 MHZ) power to acoil shape electrode under 1 Pa. A dry etching device with ICP (ModelE645-ICP) produced by Matsushita Electric Industrial Co. Ltd. is usedhere. A 150 W RF (13.56 MHZ) power is also applied to the substrate side(test piece stage) to effectively apply a negative self-bias voltage.The W film is etched with the first etching conditions, and the endportion of the second conductive layer is formed into a tapered shape.In the first etching conditions, the etching rate for W is 200.39nm/min, the etching rate for TaN is 80.32 nm/min, and the selectivity ofW to TaN is about 2.5. Further, the taper angle of W is about 26° withthe first etching conditions.

Thereafter, as shown in FIG. 8B, the first etching conditions arechanged into the second etching conditions without removing the masks309 to 312 made of resist, a mixed gas of CF₄ and Cl₂ is used as anetching gas, the gas flow rate is set to 30/30 sccm, and plasma isgenerated by applying a 500 W RF (13.56 MHZ) power to a coil shapeelectrode under 1 Pa to thereby perform etching for about 30 seconds. A20 W RF (13.56 MHZ) power is also applied to the substrate side (testpiece stage) to effectively a negative self-bias voltage. The W film andthe TaN film are both etched on the same order with the second etchingconditions in which CF₄ and Cl₂ are mixed. In the second etchingconditions, the etching rate for W is 58.97 nm/min, and the etching ratefor TaN is 66.43 nm/min. Note that, the etching time may be increased byapproximately 10 to 20% in order to perform etching without any residueon the gate insulating film.

In the first etching process, the end portions of the first and secondconductive layers are formed to have a tapered shape due to the effectof the bias voltage applied to the substrate side by adopting mask ofresist with a suitable shape. The angle of the tapered portions may beset to 15° to 45°. Thus, first shape conductive layers 314 to 317 (firstconductive layers 314 a to 317 a and second conductive layers 314 b to317 b) constituted of the first conductive layers and the secondconductive layers are formed by the first etching process. Referencenumeral 319 denotes a gate insulating film, and regions of the gateinsulating film which are not covered by the first shape conductivelayers 314 to 317 are made thinner by approximately 20 to 50 nm byetching.

Then, a first doping process is performed to add an impurity element forimparting an n-type conductivity to the semiconductor layer withoutremoving the mask made of resist (FIG. 8B). Doping may be carried out byan ion doping method or an ion injecting method. The condition of theion doping method is that a dosage is 1×10¹³ to 5×10¹⁵ atoms/cm², and anacceleration voltage is 60 to 100 keV. In this embodiment, the dosage is1.5×10¹⁵ atoms/cm² and the acceleration voltage is 80 keV. As theimpurity element for imparting the n-type conductivity, an element whichbelongs to group 15 of the periodic table, typically phosphorus (P) orarsenic (As) is used, and phosphorus (P) is used here. In this case, theconductive layers 314 to 317 become masks to the impurity element forimparting the n-type conductivity, and high concentration impurityregions 320 to 323 are formed in a self-aligning manner. The impurityelement for imparting the n-type conductivity is added to the highconcentration impurity regions 320 to 323 in the concentration range of1×10²⁰ to 1×10²¹ atoms/cm³.

Thereafter, the second etching process is performed without removing themasks made of resist as shown in FIG. 8C. Here, a mixed gas of CF₄, Cl₂and O₂ is used as an etching gas, the gas flow rate is set to 20/20/10sccm, and plasma is generated by applying a 500 W RF (13.56 MHZ) powerto a coil shape electrode under 1 Pa to thereby perform etching. A 20 WRF (13.56 MHZ) power is also applied to the substrate side (test piecestage) to effectively apply a negative self-bias voltage. In the secondetching process, the etching rate for W is 124.62 nm/min, the etchingrate for TaN is 20.67 nm/min, and the selectivity of W to TaN is 6.05.Accordingly, the W film is selectively etched. The taper angle of W is70° in the second etching. Second conductive layers 324 b to 327 b areformed by the second etching process. On the other hand, the firstconductive layers 314 a to 317 a are hardly etched, and first conductivelayers 324 a to 327 a are formed.

Next, a second doping process is performed. Second conductive layers 324b to 327 b are used as masks to an impurity element, and doping isperformed such that the impurity element is added to the semiconductorlayer below the tapered portions of the first conductive layers. In thisembodiment, phosphorus (P) is used as the impurity element, and plasmadoping is performed with the dosage of 1.5×10¹⁴ atoms/cm², the currentdensity of 0.5 μA and the acceleration voltage of 90 keV. Thus, lowconcentration impurity regions 329 to 332, which overlap with the firstconductive layers, are formed in a self-aligning manner. Theconcentration of phosphorus (P) in the low concentration impurityregions 329 to 332 is 1×10¹⁷ to 5×10¹⁸ atoms/cm³, and has a gentleconcentration gradient in accordance with the film thickness of thetapered portions of the first conductive layers. Note that, in thesemiconductor layer that overlaps with the tapered portions of the firstconductive layers, the concentration of the impurity element slightlyfalls from the end portions of the tapered portions of the firstconductive layers toward the inner portions. The concentration, however,keeps almost the same level. Further, the high concentration impurityregions 333 to 336 is formed, where the high concentration impurityelements are doped.

Thereafter, a third etching process is performed by a photolithographymethod without removing the masks made of resist as shown in FIG. 9B.The tapered portions of the first conductive layers are partially etchedto thereby form the regions that overlap with the second conductivelayer in the third etching process. However, the mask 338 from resist isformed as shown in FIG. 9B in region where the third etching is notperformed.

In the third etching process, a mixed gas of Cl₂ and SF₆ is used as anetching gas, the gas flow rate is set to 10/50 sccm, and ICP etchingmethod is used as same as first and second etching to perform the thirdetching process under above condition. In the third etching process, theetching rate for TaN is 111.2 nm/min, and the etching rate for a gateinsulating film is 12.8 nm/min.

In this embodiment, plasma is generated by applying a 500 W RF (13.56MHZ) to a coil shape electrode under 1.3 Pa to thereby perform etching.A 10 W RF (13.56 MHZ) power is also applied to the substrate side (testpiece stage) to effectively apply a negative self-bias voltage.Accordingly the first conductive layers 340 a to 342 a is formed.

In accordance with the third etching process, impurity regions (LDDregions) 343 to 345 are formed, which do not overlap with the firstconductive layers 340 a to 342 a. Note that, impurity regions (GOLDregions) 346 remain overlapped with the first conductive layer 324 a.

The electrode formed of the first conductive layer 324 a and the secondconductive layer 324 b becomes agate electrode of an n-channel TFT of adriving circuit to be formed in the later process. The electrode formedof the first conductive layer 340 a and the second conductive layer 340b becomes agate electrode of a p-channel TFT of the driving circuit tobe formed in the later process.

Similarly, the electrode formed of the first conductive layer 341 a andthe second conductive layer 341 b becomes a gate electrode of ann-channel TFT of a pixel portion to be formed in the later process, andthe electrode formed of the first conductive layer 342 a and the secondconductive layer 342 b becomes a gate electrode of a p-channel TFT ofthe pixel portion to be formed in the later process.

In accordance with the above processes, in this embodiment, the impurityregions (LDD region) 343 to 345 that do not overlap with the firstconductive layers 340 a to 342 a and the impurity region (GOLD region)346 that overlap with the first conductive layer 324 a can be formedsimultaneously, and formed corresponding to TFT characteristics.

Next, the third etching process is performed to the gate insulating film319. Here, CHF₃ is used as an etching gas, and a reactive etching method(RIE method) is used. In this embodiment, the third etching process isperformed with the chamber pressure of 6.7 Pa, the RF power of 800 W,the CHF₃ gas flow rate of 35 sccm.

Therefore, the a part of the high concentration impurity regions 333 to336 is exposed and the insulating films 356 a to 356 d.

Next, the masks of resist are removed, masks 348 and 349 are newlyformed of resist, and a third doping process is performed. In accordancewith the third doping process, impurity regions 350 to 355 are formed,in which the impurity element imparting a conductivity (p-type) oppositeto the above conductivity (n-type) is added to the semiconductor layerthat becomes an active layer of the p-channel TFT (FIG. 9C). The firstconductive layers 340 a and 342 a are used as masks to the impurityelement, and the impurity element that imparts the p-type conductivityis added to thereby form impurity regions in a self-aligning manner.

In this embodiment, the impurity regions 350 to 355 are formed by an iondoping method using diborane (B₂H₆). Note that, in the third dopingprocess, the semiconductor layer to become the n-channel TFT is coveredwith the masks 348 and 349 formed of resist. Although phosphorus isadded to the impurity regions 350 and 353 to become the p-channel TFT ofthe source region and the drain region at different concentrations inaccordance with the first and second doping processes, the dopingprocess is performed such that the concentration of the impurity elementimparting p-type conductivity is in the range of 2×10²⁰ to 2×10²¹atoms/cm³ in any of the impurity regions.

In accordance with the above-described processes, the impurity regionsare formed in the respective semiconductor layers.

Subsequently, the masks 348 and 349 of resist are removed, and a firstinterlayer insulating film 357 is fainted. This first interlayerinsulating film 357 is formed of an insulating film containing siliconby a plasma CVD method or a sputtering method into a thickness of 100 to200 nm. In this embodiment, a silicon nitride oxide film with a filmthickness of 150 nm is formed by a plasma CVD method. Of course, thefirst interlayer insulating film 357 is not particularly limited to thesilicon nitride oxide film, but an other insulating film containingsilicon may be formed into a single layer or a lamination structure.

Then, as shown in FIG. 10A, a step of activating the impurity elementsadded in the respective semiconductor layers is performed. Thisactivation step is carried out by thermal annealing using a furnaceannealing oven. The thermal annealing may be performed in a nitrogenatmosphere containing an oxygen content of 1 ppm or less, preferably 0.1ppm or less, at 400 to 700° C., typically 500 to 550° C. In thisembodiment, a heat treatment at 550° C. for 4 hours is carried out. Notethat, except the thermal annealing method, a laser annealing method, ora rapid thermal annealing method (RTA method) can be applied thereto.

Note that, in this embodiment, at the same time as the above activationprocess, nickel used as the catalyst in crystallization is gettered tothe impurity regions (334 to 336, 350 and 351) containing phosphorous ata high concentration. As a result, nickel concentration of thesemiconductor layer which becomes a channel forming region is mainlylowered. The TFT with a channel forming region thus formed has an offcurrent value decreased, and has high electric field mobility because ofgood crystallinity, thereby attaining satisfactory characteristics.

The activation may be carried out before the first interlayer insulatingfilm is formed. However, if the material used for the wiring is weakagainst heat, it is preferred to conduct activation after the interlayerinsulating film (an insulating film containing silicon as mainingredient, e.g., a silicon nitride film) as in this embodiment in orderto protect the wiring and others as well.

Besides, a doping method is performed after an activation processthereby to form a first interlayer insulating film.

In addition, heat treatment at 300 to 550° C. for 1 to 12 hours isperformed in an atmosphere containing hydrogen of 3 to 100%, to performa step of hydrogenating the semiconductor layers. In this embodiment,the heat treatment is performed at 410° C. for 1 hour in an atmospherecontaining hydrogen of about 3%. This step is a step of terminatingdangling bonds in the semiconductor layer with hydrogen in theinterlayer insulating film. As another means for hydrogenation, plasmahydrogenation (using hydrogen excited by plasma) may be carried out.

Besides, in the case of using a laser annealing method as the activationprocess, it is preferred to irradiate laser light such as an excimerlaser or a YAG laser after the hydrogenating process.

Next, as shown in FIG. 10B, a second interlayer insulating film 358 isformed on the first interlayer insulating film 357 from an organicinsulating material. In this embodiment, an acrylic resin film with athickness of 1.6 mm is formed. Patterning is then performed to formcontact holes respectively reaching the impurity regions 333, 335, 350,and 351.

A film of an insulating material containing silicon or of a film of anorganic resin can be used as the second interlayer insulating film 358.Examples of the usable insulating material containing silicon includesilicon oxide, silicon nitride, and silicon oxynitride. Examples of theusable organic resin include polyimide, polyamide, acrylic, and BCB(benzocyclobutene).

In this embodiment, a silicon oxynitride film is formed by plasma CVD.The thickness of the silicon oxynitride film is desirably 1 to 5 mm(more desirably 2 to 4 mm). A silicon oxynitride film, with its smallwater content, is effective in limiting the degradation of the ELelement.

The contact holes can be formed by dry etching or wet etching.Considering the problem of electrostatic discharge damage in etching,wet etching is desirable.

When forming the contact holes here, the first interlayer insulatingfilm and the second interlayer insulating film are etched at the sametime. Then taking the shape of the contact holes into calculation, apreferable material for the second interlayer insulating film has anetching rate faster than the etching rate of the material of the firstinterlayer insulating film.

Thus obtained are wiring lines 359 to 366 electrically connected to theimpurity regions 333, 335, 350 and 351, respectively. A laminate of a Tifilm with a thickness of 50 nm and an alloy film (an alloy film of Aland Ti) with a thickness of 500 nm is then formed by patterning. Otherconductive films may be formed instead.

Next, a transparent conductive film is formed on the laminate to athickness of 80 to 120 nm and patterned to form a transparent electrode367. (FIG. 10B)

The transparent conductive film used as the transparent electrode inthis embodiment is an indium oxide-tin (ITO) film or an indium oxidefilm with 2 to 20% of zinc oxide (ZnO) mixed thereto.

The transparent electrode 367 is formed so as to directly overlap withthe drain wiring line 365, thereby establishing an electric connectionwith a drain region of an EL driving TFT.

As shown in FIG. 11A, an insulating film containing silicon (a siliconoxide film, in this embodiment) is next formed to a thickness of 500 nm.An opening is formed in the insulating film at a position correspondingto the transparent electrode 367 to form a third interlayer insulatingfilm 368 functioning as a bank. When the opening is formed, side wallsthereof can readily be tapered by wet etching. If the side walls of theopening are not gentle enough, the level difference causes a seriousdegradation of the EL layer. Therefore the opening has to be formed witha great care.

Although a silicon oxide film is used as the third interlayer insulatingfilm in this embodiment, an organic resin film such as a polyimide film,a polyamide film, an acrylic film, or a BCB (benzocyclobutene) film maybe used in some cases.

Next, an EL layer 369 is formed by evaporation as shown in FIG. 11, andfurther a cathode (an MgAg electrode) 370 and a protective electrode 371are then formed by evaporation. Prior to forming the EL layer 369 andthe cathode 370, the transparent electrode 367 is preferably subjectedto heat treatment to remove moisture completely. The cathode of the ELelement, the MgAg electrode in this embodiment, may be formed of otherknown materials.

The EL layer 369 can be formed of known materials. The EL layer in thisembodiment has a two-layer structure consisting of a hole transportinglayer and a light emitting layer. However, a hole injection layer, anelectron injection layer or an electron transporting layer may be addedto the two-layer structure. There have been proposed variouscombinations of the layers for the EL layer, and any one of them can beused in this embodiment.

Polyphenylene vinylene in this embodiment is formed by evaporation totransform into the hole transporting layer. The light emitting layer inthis embodiment is formed by evaporation of polyvinyl carbazolemolecular-dispersed with 30 to 40% of PBD of 1,3,4-oxadiazolederivative, and doping the film with about 1% of coumarin 6 as thecenter of green light emission.

Although a protective electrode 371 alone can protect the EL layer 369from moisture and oxygen, it is more desirable to form a passivationfilm 372. In this embodiment, a silicon nitride film with a thickness of300 nm is formed as the passivation film 372. The passivation film alsocan be formed successively without exposing the device to the air afterthe protective electrode 371 is formed.

The protective electrode 371 is provided to prevent degradation of thecathode 370, and typically is a metal film containing aluminum as itsmain ingredient. Needless to say, other materials can be used for theelectrode. The EL layer 369 and the cathode 370 are very weak againstmoisture. Therefore it is desirable to protect the EL layer from theoutside air by successively forming the films up through formation ofthe protective electrode 371 without exposing the device to the air.

An appropriate thickness of the EL layer 369 is 10 to 400 nm (typically60 to 150 nm), and an appropriate thickness of the cathode 370 is 80 to200 nm (typically 100 to 150 nm).

Thus completed is an EL display device structured as shown in FIG. 11.In the process of manufacturing an EL display device according to thisembodiment, due to the circuit structure and process, source signallines are formed from Ta and W that are materials of the gate electrodewhereas gate signal lines are formed from Al that is a wiring materialfor foaming the source and drain electrode. However, the source signallines and the gate signal lines may be formed from other materials.

A driving circuit 506 having an n-channel TFT 501 and a p-channel TFT502 can be formed on the same substrate on which a pixel portion 507having a switching TFT 503, an EL driving TFT 504.

The n-channel TFT 501 of the driving circuit 506 has a channel formationregion 380; a low concentration impurity region 329 overlapping with afirst conductive layer 324 a that constitutes a part of a gate electrode(GOLD region); and a high concentration impurity region 333 functioningas a source region or a drain region. The p-channel TFT 502 has achannel formation region 373; an impurity region 352 not overlappingwith a first conductive layer 340 a that constitutes apart of a gateelectrode; and an impurity region 350 functioning as a source region ora drain region.

The switching TFT 503 of the pixel portion 507 has a channel formationregion 374; a low concentration impurity region 344 not overlapping witha first conductive layer 341 a formed outside the gate electrode (LDDregion); and a high concentration impurity region 335 functioning as asource region or a drain region.

The EL driving TFT 504 of the pixel portion 507 has a channel formationregion 375; an impurity region 353 not overlapping a first conductivelayer 327 a which is structuring apart of the gate electrode; a highconcentration impurity region 351 functioning as a source region or adrain region.

Embodiment 6

This embodiment deals with the fabrication of the EL display deviceaccording to the invention with reference to FIGS. 16 and 17.

FIG. 16(A) is a top view of a TFT substrate in the EL display deviceaccording to this invention. In this specification, the TFT substratestands for a substrate on which the pixel unit is provided.

On the substrate 4001 are provided the pixel unit 4002, the sourcesignal line drive circuit 4003, the first gate signal line drive circuit4004 a and the second gate signal line drive circuit 4004 b. In thisinvention, the numbers of the source signal line drive circuits and ofthe gate signal line drive circuits are not limited to the numbers shownin FIG. 16(A). The numbers of the source signal line drive circuits andof the gate signal line drive circuits can be suitably set by adesigner. In this Example, further, though the source signal line drivecircuits and the gate signal line drive circuits are provided on the TFTsubstrate, the invention is in no way limited to this constitution only.The source signal line drive circuits and the gate signal line drivecircuits provided on a substrate separate from the TFT substrate may beelectrically connected to the pixel unit through external connectionterminals such as FPC or TAB.

Reference numeral 4005 a denotes a detour wiring connected to the powersource feed lines (not shown) provided on the pixel unit 4002, referencenumeral 4005 b denotes a detour wiring for gates connected to the firstand second gate signal line drive circuits 4004 a and 4004 b, andreference numeral 4005 c denotes a detour wiring for sources connectedto the source signal line drive circuit 4003.

The detour wiring 4005 b for gates and the detour wiring 4005 c forsources are connected to an IC or the like on the outside of thesubstrate 4001 through the FPCs 4006. Further, the detour wiring 4005 ais connected to the power source on the outside of the substrate 4001through the FPC 4006.

FIG. 16(B) is a view illustrating the detour wiring 4005 a on anenlarged scale, wherein 4100 denotes a detour wiring for R, 4101 denotesa detour wiring for G, and 4102 denotes a detour wiring for B.

If it is presumed that the ratio of the current density in the EL layerof the EL element for R, current density in the EL layer of the ELelement for G and current density in the EL layer of the EL element forB, is 1.15:1.29:1, then, it is important in the invention that the widthWr of the detour wiring 4100 for R, the width Wg of the detour wiring1401 for G and the width Wb of the detour wiring 4102 for B areWg>Wr>Wb. More preferably from the formula 3 in the embodiment, Wr:Wg:Wb1.15:1.29:1.

The above constitution of this invention makes it possible to obtain abalance in the light-emitting brightnesses of the pixels R, G and B.

FIG. 17(A) is a top view of the EL display device formed by sealing theTFT substrate shown in FIG. 16(A) with a sealing member, FIG. 17(B) is asectional view along A-A′ in FIG. 17(A), and FIG. 17(C) is a sectionalview along B-B′ in FIG. 17(A). Those shown already in FIG. 16 aredenoted by the same reference numerals.

The sealing member 4009 is so provided as to surround the pixel unit4002, source signal line drive circuit 4003, and first and second gatesignal line drive circuits 4004 a, 4004 b formed on the substrate 4001.Further, a sealing member 4008 is provided on the pixel unit 4002, onthe source signal line drive circuit 4003 and on the first and secondgate signal line drive circuits 4004 a, 4004 b. Accordingly, the pixelunit 4002, source signal line drive circuit 4003, and first and secondgate signal line drive circuits 4004 a, 4004 b are sealed with a fillermaterial 4210 being surrounded by the substrate 4001, sealing member4009 and sealing member 4008.

Plural TFTs are possessed by the pixel unit 4002, by the source signalline drive circuit 4003 and by the first and second gate signal linedrive circuits 4004 a, 4004 b formed on the substrate 4001. FIG. 17(B)representatively illustrates drive TFTs (here, an n-channel TFT and ap-channel TFT) 4201 formed on the underlying film 4010 and included inthe source signal line drive circuit 4003, and EL drive TFT (TFT forcontrolling the current flowing into the EL element) 4202 included inthe pixel unit 4002.

In this embodiment, the drive TFT 4201 is a p-channel TFT or ann-channel TFT fabricated by a known method, and the EL drive TFT 4202 isa p-channel TFT fabricated by a known method. Further, the pixel unit4002 is provided with a holding capacity (not shown) connected to thegate of the EL drive TFT 4202.

An interlayer insulating film (flattened film) 4301 is formed on thedrive TFT 4201 and on the EL drive TFT 4202, and on which is formed apixel electrode (anode) 4203 electrically connected to the drain of theEL drive TFT 4202. As the pixel electrode 4203, there is used atransparent electrically conducting film having a large work function.As the transparent electrically conducting film, there can be used acompound of indium oxide and tin oxide, a compound of indium oxide andzinc oxide, zinc oxide, tin oxide or indium oxide. It is also allowableto add gallium to the transparent electrically conducting film.

An insulating film 4302 is formed on the pixel electrode 4203. Anopening is formed in the insulating film 4302 on the pixel electrode4203. An EL (electroluminescence) layer 4204 is formed in the opening onthe pixel electrode 4203. The EL layer 4204 may be made of a knownorganic EL material or an inorganic EL material. Further, the organic ELmaterial may be either a low-molecular (monomeric) material or a highmolecular (polymeric) material.

The EL layer 4204 may be formed by a known deposition technology or acoating technology. Further, the EL layer may have a laminated-layerstructure of a positive hole-injection layer, a positivehole-transporting layer, a light-emitting layer, and anelectron-transporting layer or an electron injection layer, or may havea single-layer structure.

On the EL layer 4204 is formed a cathode 4205 comprising an electricallyconducting film (typically, an electrically conducting film comprisingchiefly aluminum, copper or silver, or a laminated-layer film thereofwith other electrically conducting films) having light-shieldingproperty. It is desired that water and oxygen are removed as much aspossible from the interface between the cathode 4205 and the EL layer4204. It is therefore necessary to make such a contrivance that the ELlayer 4204 is formed in a nitrogen or a rare gas atmosphere, and thecathode 4205 is formed while being kept away from oxygen and water. Inthis embodiment, the film is formed as described above by using afilm-forming device of the multi-chamber type (cluster tool type). Apredetermined voltage is given to the cathode 4205.

There is thus formed an EL element 4303 comprising the pixel electrode(anode) 4203, EL layer 4204 and cathode 4205. A protection film 4303 isformed on the insulating film 4302 so as to cover the EL element 4303.The protection film 4303 is effective in preventing oxygen and waterfrom entering into the EL element 4303.

Reference numeral 4005 a is a detour wiring connected to the powersource feed wiring, and is electrically connected to the source regionof the EL drive TFTs 4202. The detour wiring 4005 a is electricallyconnected to the FPC wiring 4301 possessed by the FPC 4006 passingthrough between the sealing member 4009 and the substrate 4001 and viaan anisotropic electrically conducting film 4300.

As the sealing member 4008, there can be used a glass member, a metalmember (representatively, a stainless steel member), a ceramic member ora plastic member (inclusive of a plastic film). As the plastic member,there can be used an FRP (Fiberglass-Reinforced Plastic) plate, a PVF(polyvinyl fluoride) film, a Mylar film, a polyester film, or an acrylicresin film. It is also allowable to use a sheet of a structure in whichan aluminum foil is sandwiched by the PVF films or the Mylar films.

When light emitted from the EL element is directed toward the covermember, however, the cover member must be transparent. In this case, useis made of a transparent material such as glass plate, a plastic plate,a polyester film or an acrylic film.

As the filler material 4210, there can be used an ultraviolet-raycurable resin or a thermosetting resin in addition to the inert gas suchas nitrogen or argon. Namely, there can be used a PVC (polyvinylchloride), an acrylic resin, a polyimide, an epoxy resin, a siliconeresin, a PVB (polyvinyl butyral) or an EVA (ethylenevinyl acetate). Inthis embodiment, nitrogen is used as the filler material.

In order to have the filler material 4210 exposed to a hygroscopicmaterial (preferably, barium oxide) or a material capable of adsorbingoxygen, further, a recessed portion 4007 is formed in the sealing member4008 on the side of the substrate 4001, and the hygroscopic material orthe material 4207 capable of adsorbing oxygen is disposed therein. Thehygroscopic material or the material 4207 capable of adsorbing oxygen isheld in the recessed portion 4007 by a recessed portion-covering member4208, so that the hygroscopic material or the material 4207 capable ofadsorbing oxygen will not scatter. The recessed portion-covering member4208 is of the form of a fine mesh which permits the air or water topass through but does not permit the passage of the hygroscopic materialor the material 4207 that adsorbs oxygen. Provision of the hygroscopicmaterial or the material 4207 capable of adsorbing oxygen suppresses thedeterioration of the EL element 4303.

Referring to FIG. 17(C), the electrically conducting film 4203 a isformed to come in contact onto the detouring wiring 4005 asimultaneously with the formation of the pixel electrode 4203.

The anisotropic film 4300 has an electrically conducting filler 4300 a.Upon thermally adhering the substrate 4001 and the FPC 4006 together,the electrically conducting film 4203 a on the substrate 4001 and thewiring 4301 for FPC on the FPC 4006 are electrically connected togetherthrough the electrically conducting filler 4300 a.

This embodiment can be carried out in free combination with theembodiments 1 to 5.

Embodiment 7

This embodiment deals with an example in which the TFT and the ELelement are sealed on the substrate with a sealing member, and thesubstrate is replaced, while making a reference to FIG. 18 which is asectional view illustrating the steps of fabricating the pixel unit.

In FIG. 18(A), reference numeral 3101 is a substrate on which theelements are to be formed (hereinafter referred to as element-formingsubstrate) and on which a peeling layer 3102, which is an amorphoussilicon film, is formed maintaining a thickness of 100 to 500 nm (300 nmin this embodiment). In this embodiment, a glass substrate is used as anelement-forming substrate 3101. It is, however, also allowable to use aquartz substrate, a silicon substrate, a metal substrate (SUS substrate)or a ceramic substrate.

The peeling layer 3102 may be formed by a reduced pressure thermal CVDmethod, a plasma CVD method, a sputtering method or a vapor depositionmethod. On the peeling layer 3102 is formed an insulation film 3103comprising a silicon oxide film maintaining a thickness of 200 nm. Theinsulating film 3103 may be formed by a reduced pressure thermal CVDmethod, a plasma CVD method, a sputtering method or a vapor depositionmethod.

On the insulating film 3103 are formed a switching TFT 3104 and an ELdrive TFT 3105 of the pixel unit. Though this embodiment has dealt withan example in which the switching TFT 3104 is an n-channel TFT and theEL drive TFT 3105 is a p channel TFT, it should be noted that theembodiment is not limited to this constitution only. The switching TFT3104 and the EL drive TFT 3105 may be either the p-channel TFTs or the nchannel TFTs.

In this embodiment, further, the switching TFT 31Q4 has a double gatestructure. However, the switching TFT is not limited to this structureonly but may be of a single gate structure or of any other multi-gatestructure. Upon employing the double gate structure as in thisembodiment, the two channel-forming regions are connected in seriesmaking it possible to effectively suppress the off current (current thatflows when the TFT is turned off).

The first interlayer insulating film 3107 is formed on the switching TFT3104 and on the EL drive TFT 3105. The first interlayer insulating film3107 is formed to cover the switching TFT 3104 and the EL drive TFT3105, so that a pixel electrode 3106 that will be formed later will beflattened.

Further, the pixel electrode 3106 is so formed as is electricallyconnected to the drain region of the EL drive TFT 3105. In thisembodiment, the pixel electrode 3106 is formed by patterning atransparent electrically conducting film (typically, a compound film ofindium oxide and tin oxide) formed maintaining a thickness of 100 nm.The pixel electrode 3106 works as an anode of the EL element.

After the pixel electrode 3106 is formed, the second interlayerinsulating film 3114, which is a silicon oxide film, is formedmaintaining a thickness of 300 nm. Then, an opening 3108 is formed,followed by the formation of an EL layer 3109 maintaining a thickness of70 nm and a cathode 3110 maintaining a thickness of 300 nm by vapordeposition method. This embodiment uses the EL layer 3109 of a structurelaminating a positive hole-injection layer of a thickness of 20 nm and alight emitting layer of a thickness of 50 nm. It is of course allowableto use any other known structure combining the light emitting layer witha positive hole-injection layer, a positive hole-transporting layer, anelectron-transporting layer or an electron-injection layer.

There is thus formed the EL element 3111 comprising the pixel electrode(anode) 3106, EL layer 3109 and cathode 3110. In this embodiment, the ELelement 3111 works as a light emitting element.

Next, a substrate (hereinafter referred to as sealing member) 3113 isstuck for securing the element with a first adhesive 3112. In thisembodiment, a flexible plastic film is used as the sealing member 3113.It is, however, also allowable to use a glass substrate, a quartzsubstrate, a plastic substrate, a silicon substrate or a ceramicsubstrate. The first adhesive 3112 must be the one that gives theselection ratio when the peeling layer 3102 is removed later.

Typically, there may be used an insulating film of a resin. Though thisembodiment uses a polyimide, there may be further used an acrylic resin,a polyamide or an epoxy resin. When it is positioned on the side of theobserver (on the side of the user of the light-emitting device) asviewed from the EL element, it must be made of a material that transmitslight.

The EL element can be completely shut off the open air by the firstadhesive 3112. This nearly completely suppresses the organic EL materialfrom being deteriorated by oxygen, and reliability of the EL element isgreatly improved.

Referring next to FIG. 18(B), the peeling layer 3102 is removed, and theelement-forming substrate 3101 and the insulating film 3103 are peeledoff. In this embodiment, the peeling layer 3102 is exposed to a gascontaining halogen fluoride and is peeled off. In this embodiment,chlorine trifluoride (ClF#(3)) is used as halogen fluoride and nitrogenis used as a dilution gas. As the dilution gas, there may be furtherused argon, helium or neon. The flow rate may be 500 sccm (8.35×10⁻⁶m³/s), and the reaction pressure may be 1 to 10 Torr (1.3×10² to 1.3×10³Pa). The treating temperature may be room temperature (typically, 20 to27° C.).

In this case, the silicon film is etched. However, the plastic film,glass substrate, polyimide film and silicon oxide film are not etched.That is, upon being exposed to the chlorine trifluoride gas, the peelinglayer 3012 is selectively etched and is, then, completely removed. Theactive layer for the switching TFT 3104 and the EL drive TFT 3105, whichis similarly formed of the silicon film, is covered with the firstinterlayer insulating film 3107 and is not exposed to the chlorinetrifluoride gas and is not etched.

In the case of this embodiment, the peeling layer 3102 is graduallyetched from the exposed end portion and at a moment when it iscompletely removed, the element-forming substrate 3101 and theinsulating film 3103 are separated from each other. Here, the TFT andthe EL element have been formed by laminating thin films, and remain ina form being transferred onto the sealing member 3113.

Here, the peeling layer 3102 starts etched from the end portion. As theelement-forming substrate 3101 becomes large, however, an extendedperiod of time is required until it is completely removed, which is notdesirable. When removed by etching, therefore, the element-formingsubstrate 3101 should not have a diagonal size of larger than 3 inches(preferably, should not have a diagonal size of larger than 1 inch).

In this embodiment, the peeling layer 3102 is removed by etching in anatmosphere of a chlorine trifluoride gas. The embodiment, however, isnot limited to this constitution only. The element-forming substrate3101 may be peeled off by irradiating the peeling layer 3102 with alaser beam from the side of the element-forming substrate 3101 tovaporize the peeling layer 3102. In this case, the kind of the laserbeam and the material of the element-forming substrate, 3101 must besuitably selected so that the laser beam passes through theelement-forming substrate 3101. When a quartz substrate is used as theelement-forming substrate 3101, for example, a linear beam is formed byusing a YAG laser (fundamental wave (1046 nm), second harmonic (532 nm),third harmonic (355 nm), fourth harmonic (266 nm)) or by using anexcimer laser (wavelength 308 nm) which is projected to penetratethrough the quartz substrate. The excimer laser does not pass throughthe glass substrate. When the glass substrate is used as the elementforming substrate 3101, therefore, the linear beam is fainted by usingthe fundamental wave of the YAG laser, second harmonic, or thirdharmonic or, preferably, second harmonic (wavelength, 532 nm) topenetrate through the glass substrate.

When the peeling is to be effected by using a laser beam, the peelinglayer 3102 is formed of a material that vaporizes upon the irradiationwith the laser beam.

In addition to using the laser beam, the element forming substrate 3101may be peeled off by dissolving the peeling layer 3102 with a solution.In this case, it is desired to use such a solution which selectivelydissolves the peeling layer 3102 only.

Thus, after the TFT and the EL element are transferred onto the sealingmember 3113, a second adhesive 3114 is formed and to which a secondelement-forming substrate 3115 is stuck as shown in FIG. 18(C). As thesecond adhesive 3114, there may be used an insulating film of a resin(typically, a polyimide, an acrylic resin, a polyamide or an epoxyresin) or an inorganic insulating film (typically, a silicon oxidefilm). When it is positioned on the side of the observer as viewed fromthe EL element, it must be composed of a material that transmits light.

Thus, the TFT and the EL element are transferred from theelement-forming substrate 3101 to the second element-forming substrate3115. As a result, there is obtained an EL display device sandwichedbetween the sealing member 3113 and the second element-forming substrate3115. Here, if the sealing member 3113 and the second element-formingsubstrate 3115 are formed of the same material, the coefficient ofthermal expansion becomes the same, and the device receives littleeffect of stress and strain caused by a change in the temperature.

In the EL display device fabricated according to this embodiment, thematerials of the sealing member 3113 and the material of the secondelement-forming substrate 3115 can be selected without the need oftaking into consideration the heat resistance during the processing ofthe TFTs. For example, a plastic substrate can be used as the sealingmember 3113 and as the second element-forming substrate 3115 tofabricate a flexible EL display device.

This embodiment can be carried out in free combination with theconstitutions of the embodiments 1 to 6.

Embodiment 8

This embodiment deals with an example of forming a DLC film on the wholesurfaces of the EL display device or on the end of the EL displaydevice.

FIG. 19(A) is a sectional view of the EL display device having the DLCfilm formed on the whole surfaces thereof. A switching TFT 3205 and anEL drive TFT 3204 are formed on the substrate 3201. Reference numeral3203 denotes an EL element, and a current that flows into the EL element3203 is controlled by the EL drive TFT 3204.

The switching TFT 3205, EL drive TFT 3204 and EL element 3207 are sealedby a sealing member 3202 and a sealing member 3208, and are shut offfrom the external air. Reference numeral 3209 denotes a detour wiringexposed out of space in which the EL element 3207 is sealed, passingthrough between the sealing member 3208 and the substrate 3201.

Reference numeral 3210 denotes a DLC film covering the entire EL displaydevice except a portion of the detour wiring 3209 that is exposed out ofspace in which the EL element 3203 is sealed.

In this embodiment, the DLC film may be formed by an ECR plasma CVDmethod, an RF plasma CVD method, a μ-wave plasma CVD method or asputtering method. The DLC film has a feature in that it exhibits anasymmetrical peak near at 1550 cm⁻¹ and a Raman spectral distributionhaving a shoulder near 1300 cm⁻¹. It further has a feature of exhibitinga hardness of 15 to 25 GPa when measured by using a microhardnesstester. Such a carbon film protects the surface of the substrate. Inparticular, since the plastic substrate easily gets scratched, coveringthe surface with the DLC film as shown in FIG. 19(A) is effective inpreventing scars.

The DLC film is effective in preventing the infiltration of oxygen andwater. In forming the DLC film 3210 so as to cover the sealing member3208 as in this embodiment, therefore, it is allowed to prevent thematters that deteriorate the EL layer, such as water and oxygen, fromentering into space in which the EL element 3204 is sealed.

In forming the DLC film 3210, further, part of the detour wiring 3209exposed out of space in which the EL element 3203 is sealed, is coveredwith a resist mask which is then removed after the DLC film 3210 hasbeen formed. Part of the detour wiring 3209 not covered with the DLCfilm 3210 is connected to the wiring 3211 for FPC provided in the FPC3211 through an anisotropic electrically conducting film 3213.

FIG. 19(B) is a sectional view of the EL display device of when the DLCfilm is formed at an end of the EL display device. A switching TFT 3305and an EL drive TFT 3304 are formed on a substrate 3301. Referencenumeral 3303 denotes an EL element, and a current flowing into the ELelement 3303 is controlled by the EL drive TFT 3304.

The switching TFT 3305, EL drive TFT 3304 and EL element 3303 are sealedby a sealing member 3302 and a sealing member 3308, and are shut offfrom the external air. Reference numeral 3309 denotes a detour wiringexposed out of space in which the EL element 3303 is sealed, passingthrough between the sealing member 3308 and the substrate 3301.

Reference numeral 3310 denotes a DLC film covering part of the sealingmember 3302, part of the substrate 3301 and the sealing member 3308except a portion of the detour wiring 3309 that is exposed out of spacein which the EL element 3303 is sealed.

The DLC film 3310 is effective in preventing the infiltration of oxygenand water. In forming the DLC film 3310 so as to cover the sealingmember 3308 as in this embodiment, therefore, it is allowed to preventthe matters that deteriorate the EL layer, such as water and oxygen,from entering into space in which the EL element 3303 is sealed.

The EL display device shown in FIG. 19(B) has the DLC film 3310 formedon the end (portion inclusive of the sealing member) only of the ELdisplay device. Therefore, the DLC film 3310 can be easily formed.

In forming the DLC film 3310, further, part of the detour wiring 3309exposed out of space in which the EL element 3303 is sealed, is coveredwith a resist mask which is then removed after the DLC film 3310 hasbeen formed. Part of the detour wiring 3309 not covered with the DLCfilm 3310 is connected to the wiring 3311 for FPC provided in the FPC3311 through an anisotropic electrically conducting film 3313.

This embodiment can be carried out in free combination with theconstitutions of the embodiments 1 to 7.

Embodiment 9

The EL display device fabricated in accordance with the presentinvention is of the self-emission type, and thus exhibits more excellentrecognizability of the displayed image in a light place as compared tothe liquid crystal display device. Furthermore, the EL display devicehas a wider viewing angle. Accordingly, the EL display device can beapplied to a display portion in various electronic devices. For example,in order to view a TV program or the like on a large-sized screen, theEL display device in accordance with the present invention can be usedas a display portion of an electro luminescence display device (i.e., adisplay in which an EL display device is installed into a frame) havinga diagonal size of 30 inches or larger (typically 40 inches or larger.)

The EL display device includes all kinds of displays to be used fordisplaying information, such as a display for a personal computer, adisplay for receiving a TV broadcasting program, a display foradvertisement display. Moreover, the EL display device in accordancewith the present invention can be used as a display portion of othervarious electric devices.

As other electronic equipments of the present invention there are: avideo camera; a digital camera; a goggle type display (head mounteddisplay); a navigation system; a sound reproduction apparatus (a caraudio stereo or an audio stereo and so forth); a notebook type personalcomputer; a game apparatus; a portable information terminal (such as amobile computer, a mobile phone, a portable game machine, or anelectronic book); and an image playback device equipped with a recordingmedium (specifically, device provided with a display portion which playsback images in a recording medium such as a digital versatile diskplayer (DVD), and displays the images). Specific examples of thoseelectronic equipments are shown in FIGS. 12A to 13B.

FIG. 12A shows an EL display device containing a casing 2001, a supportstand 2002, and a display portion 2003. The EL display device of thepresent invention can be used as the display portion 2003. Such an ELdisplay device is a self light emitting type so that a back light is notnecessary. Thus, the display portion can be made thinner than that of aliquid crystal display.

FIG. 12B shows a video camera, and contains a main body 2101, a displayportion 2102, a sound input portion 2103, operation switches 2104, abattery 2105, and an image receiving portion 2106. The EL display deviceof the present invention can be used as the display portion 2102.

FIG. 12C illustrates a portion (the right-half piece) of alight-emitting device of head mount type, which includes a main body2201, signal cables 2202, a head mount band 2203, a screen portion 2204,an optical system 2205, a display portion 2206, or the like. The ELdisplay device of the present invention is applicable to the displayportion 2206.

FIG. 12D is an image playback device equipped with a recording medium(specifically, a DVD playback device), and contains a main body 2301, arecording medium (such as a DVD and so forth) 2302, operation switches2303, a display portion (a) 2304, and a display portion (b) 2305. Thedisplay portion (a) 2304 is mainly used for displaying imageinformation. The display portion (b) 2305 is mainly used for displayingcharacter information. The EL display device of the present inventioncan be used as the display portion (a) 2304 and as the display portion(b) 2305. Note that the image playback device equipped with therecording medium includes devices such as game machines.

FIG. 12E shows a goggle type display (head mount display), and containsa main body 2401, a display portion 2402, and an arm portion 2403. TheEL display device of the present invention is applicable to the displaydevice 2402.

FIG. 12F is a personal computer, and contains a main body 2501, a casing2502, a display portion 2503, and a keyboard 2504. The EL display deviceof the present invention can be used as the display portion 2503.

Note that if the luminance of the EL material increases in the future,then it will become possible to use the EL display device of the presentinvention in a front type or a rear type projector by expanding andprojecting light containing output image information with a lens or thelike.

Further, the above electric devices display often informationtransmitted through an electronic communication circuit such as theInternet and CATV (cable tv), and particularly situations of displayingmoving images is increasing. The response speed of EL materials is sohigh that the above electric devices are good for display of movingimage.

In addition, since the EL display device conserves power in the lightemitting portion, it is preferable to display information so as to makethe light emitting portion as small as possible. Consequently, whenusing the light emitting device in a display portion mainly forcharacter information, such as in a portable information terminal, inparticular a portable telephone or an audio stereo, it is preferable todrive the EL display device so as to form character information by thelight emitting portions while non-light emitting portions are set asbackground.

FIG. 13A shows a portable telephone, and contains a main body 2601, asound output portion 2602, a sound input portion 2603, a display portion2604, operation switches 2605, and an antenna 2606. The EL displaydevice of the present invention can be used as the display portion 2604.Note that by displaying white color characters in a black colorbackground, the display portion 2604 can suppress the power consumptionof the portable telephone.

FIG. 13B shows a sound reproduction device, in a concrete term, caraudio stereo, and contains a main body 2701, a display portion 2702, andoperation switches 2703 and 2704. The EL display device of the presentinvention can be used as the display portion 2702. Further, a carmounting audio stereo is shown in this embodiment, but a portable typeor domestic type audio playback device may also be used. Note that, bydisplaying white color characters in a black color background, thedisplay portion 2702 can suppress the power consumption. It isespecially effective for a portable sound reproduction device.

As described above, the application range of this invention is extremelywide, and it may be used for electric devices in various fields.Further, the electric device of this embodiment may be obtained by usingan EL display device freely combining the structures of the first toeighth embodiments.

The constitution of this invention makes it possible to maintain abalance of light-emitting brightness of the pixels R, G and Birrespective of the number of pixels that produce the white display.

In this embodiment, further, the amplitude of the video signals may beincreased for those pixels in which a large voltage is applied to the ELelement. Owing to the above constitution, the off current of the ELdrive TFT is prevented from increasing when the voltage of the powersource feed lines is elevated.

At the same time, the channel width (W) may be increased for the ELdrive TFTs of the pixels to which are connected the power source feedlines having a large absolute current value. The above-mentionedconstitution of the invention works to suppress the deterioration of theEL drive TFTs even when the current for controlling the EL drive TFTs isincreased due to an increase in the absolute current value that flowsthrough the power source feed lines. The light-emitting brightness ofthe EL element is adjusted relying upon the voltage applied to the ELelements, and a picture of vivid colors is displayed maintaining a goodbalance in the light emitting brightnesses of red color, blue color andgreen color.

What is claimed is:
 1. A light-emitting device comprising: a substrate;a first column of first EL elements over the substrate, the first ELelements each comprising a first electrode connected to a first TFT andbeing configured to emit light of a first color; a second column ofsecond EL elements over the substrate, the second EL elements eachcomprising a second electrode electrically connected to a second TFT andbeing configured to emit light of a second color different from thefirst color; a first power source feed line over the substrate, thefirst power source feed line being configured to supply current to thefirst EL elements through the first TFTs; and a second power source feedline over the substrate, the second power source feed line beingconfigured to supply current to the second EL elements through thesecond TFTs, wherein a first width of the first power source feed lineis different from a second width of the second power source feed line.2. The light-emitting device according to claim 1, wherein the first ELelements are configured to emit red light, wherein the second ELelements are configured to emit green light, and wherein a first channelwidth of the first TFTs is different from a second channel width of thesecond TFTs.
 3. The light-emitting device according to claim 1, whereinthe first EL elements are configured to emit red light, wherein thesecond EL elements are configured to emit green light, wherein a firstchannel width of the first TFTs is greater than a second channel widthof the second TFTs, and wherein the first width of the first powersource feed line is greater than the second width of the second powersource feed line.
 4. The light-emitting device according to claim 1,further comprising: a first draw-out terminal; a second draw-outterminal; a first detour wiring; and a second detour wiring, wherein thefirst power source feed line is electrically connected to the firstdraw-out terminal through the first detour wiring, and wherein thesecond power source feed line is electrically connected to the seconddraw-out terminal through the second detour wiring.
 5. Thelight-emitting device according to claim 1, further comprising: a firstdraw-out terminal; a second draw-out terminal; a first detour wiring;and a second detour wiring, wherein the first power source feed line iselectrically connected to the first draw-out terminal through the firstdetour wiring, wherein the second power source feed line is electricallyconnected to the second draw-out terminal through the second detourwiring, and wherein a width of the first detour wiring is different froma width of the second detour wiring.
 6. A light-emitting devicecomprising: a substrate; a detour wiring; a draw-out terminal; a firstcolumn of first EL elements over the substrate, the first EL elementseach comprising a first electrode connected to a first TFT and beingconfigured to emit light of a first color; a second column of second ELelements over the substrate, the second EL elements each comprising asecond electrode electrically connected to a second TFT and beingconfigured to emit light of a second color different from the firstcolor; a first power source feed line over the substrate, the firstpower source feed line being configured to supply current to the firstEL elements through the first TFTs; and a second power source feed lineover the substrate, the second power source feed line being configuredto supply current to the second EL elements through the second TFTs,wherein a first width of the first power source feed line is differentfrom a second width of the second power source feed line, and whereinthe first power source feed line is electrically connected to thedraw-out terminal through the detour wiring.
 7. A light-emitting devicecomprising: a substrate; a detour wiring; a draw-out terminal; a firstcolumn of first EL elements over the substrate, the first EL elementseach comprising a first electrode connected to a first TFT and beingconfigured to emit light of a first color; a second column of second ELelements over the substrate, the second EL elements each comprising asecond electrode electrically connected to a second TFT and beingconfigured to emit light of a second color different from the firstcolor; a first power source feed line over the substrate, the firstpower source feed line being configured to supply current to the firstEL elements through the first TFTs; and a second power source feed lineover the substrate, the second power source feed line being configuredto supply current to the second EL elements through the second TFTs,wherein a first width of the first power source feed line is differentfrom a second width of the second power source feed line, wherein afirst channel width of the first TFTs is different from a second channelwidth of the second TFTs, and wherein the first power source feed lineis electrically connected to the draw-out terminal through the detourwiring.
 8. The light-emitting device according to claim 7, wherein thefirst EL elements are configured to emit red light, wherein the secondEL elements are configured to emit green light, and wherein the firstchannel width is greater than the second channel width.
 9. Thelight-emitting device according to claim 7, wherein the first ELelements are configured to emit red light, wherein the second ELelements are configured to emit green light, wherein the first channelwidth is greater than the second channel width, and wherein the firstwidth of the first power source feed line is greater than the secondwidth of the second power source feed line.
 10. The light-emittingdevice according to claim 6, further comprising: an additional detourwiring; an additional draw-out terminal, wherein the second power sourcefeed line is electrically connected to the additional draw-out terminalthrough the additional detour wiring.
 11. The light-emitting deviceaccording to claim 7, further comprising: an additional detour wiring;an additional draw-out terminal, wherein the second power source feedline is electrically connected to the additional draw-out terminalthrough the additional detour wiring.
 12. The light-emitting deviceaccording to claim 1, wherein the first EL elements are configured toemit red light, wherein the second EL elements are configured to emitgreen light, and wherein the first width is greater than the secondwidth.
 13. The light-emitting device according to claim 6, wherein thefirst EL elements are configured to emit red light, wherein the secondEL elements are configured to emit green light, and wherein the firstwidth is greater than the second width.
 14. The light-emitting deviceaccording to claim 7, wherein the first EL elements are configured toemit red light, wherein the second EL elements are configured to emitgreen light, and wherein the first width is greater than the secondwidth.
 15. The light-emitting device according to claim 1, wherein thefirst power source feed line and the second power source feed line areconfigured to be set at a first potential and at a second potential,respectively, the second potential being different from the firstpotential.
 16. The light-emitting device according to claim 6, whereinthe first power source feed line and the second power source feed lineare configured to be set at a first potential and a at second potential,respectively, the second potential being different from the firstpotential.
 17. The light-emitting device according to claim 7, whereinthe first power source feed line and the second power source feed lineare configured to be set at a first potential and a at second potential,respectively, the second potential being different from the firstpotential.
 18. The light-emitting device according to claim 1, furthercomprising: a third column of third EL elements over the substrate, thethird EL elements each comprising a third electrode connected to a thirdTFT and being configured to emit light of a third color different fromthe first color and the second color; and a third power source feed lineover the substrate, the third power source feed line being configured tosupply current to the third EL elements through the third TFTs, whereina third width of the third power source feed line is different from thefirst width and the second width.
 19. The light-emitting deviceaccording to claim 6, further comprising: a third column of third ELelements over the substrate, the third EL elements each comprising athird electrode connected to a third TFT and being configured to emitlight of a third color different from the first color and the secondcolor; and a third power source feed line over the substrate, the thirdpower source feed line being configured to supply current to the thirdEL elements through the third TFTs, wherein a third width of the thirdpower source feed line is different from the first width and the secondwidth.
 20. The light-emitting device according to claim 7, furthercomprising: a third column of third EL elements over the substrate, thethird EL elements each comprising a third electrode connected to a thirdTFT and being configured to emit light of a third color different fromthe first color and the second color; and a third power source feed lineover the substrate, the third power source feed line being configured tosupply current to the third EL elements through the third TFTs, whereina third width of the third power source feed line is different from thefirst width and the second width.
 21. The light-emitting deviceaccording to claim 1, further comprising: a third column of third ELelements over the substrate, the third EL elements each comprising athird electrode connected to a third TFT and being configured to emitlight of a third color different from the first color and the secondcolor; and a third power source feed line over the substrate, the thirdpower source feed line being configured to supply current to the thirdEL elements through the thirds TFTs, wherein the first column isadjacent to the second column, the second column is adjacent to thethird column, and wherein the first power source feed line, the secondpower source feed line and the third power source feed line are distinctfrom each other.
 22. The light-emitting device according to claim 6,further comprising: a third column of third EL elements over thesubstrate, the third EL elements each comprising a third electrodeconnected to a third TFT and being configured to emit light of a thirdcolor different from the first color and the second color; and a thirdpower source feed line over the substrate, the third power source feedline being configured to supply current to the third EL elements throughthe thirds TFTs, wherein the first column is adjacent to the secondcolumn, the second column is adjacent to the third column, and whereinthe first power source feed line, the second power source feed line andthe third power source feed line are distinct from each other.
 23. Thelight-emitting device according to claim 7, further comprising: a thirdcolumn of third EL elements over the substrate, the third EL elementseach comprising a third electrode connected to a third TFT and beingconfigured to emit light of a third color different from the first colorand the second color; and a third power source feed line over thesubstrate, the third power source feed line being configured to supplycurrent to the third EL elements through the thirds TFTs, wherein thefirst column is adjacent to the second column, the second column isadjacent to the third column, and wherein the first power source feedline, the second power source feed line and the third power source feedline are distinct from each other.
 24. An electronic equipmentcomprising the light-emitting device according to claim
 1. 25. Anelectronic equipment comprising the light-emitting device according toclaim
 6. 26. An electronic equipment comprising the light-emittingdevice according to claim 7.